Inductive heating-cooling apparatus and method

ABSTRACT

Sections of an induction heating coil are connected in parallel with sections of a shunt coil so that the section to section impedance of the unit differs. Accordingly, the amount of heat power applied to sections of a metal object by the heating coil is varied according to a predetermined pattern. Electric power applied to the entire shunt coil and heating coil unit is lowered over a period of time to cool the metal object progressively along a geometrical axis.

United States Patent lnventor Appl. No. Filed Patented Assignee INDUCTIVE HEATING-COOLING APPARATUS [56] References Cited UNITED STATES PATENTS 3,067,308 12/1962 McBrien 219/1015 3,153,132 10/1964 Greene 219 1075 Primary Examiner.l. V. Truhe Assistant ExaminerL. H. Bender AttameySeidel, Gonda & Goldhammer ANDMETHOD ABSTRACT: Sections of an induction heating coil are con- 3 Claims 2 Drawmg nected in parallel with sections of a shunt coil so that the sec- U.S. Cl 219/ 10.75, tion to section impedance of the unit differs. Accordingly, the 219/l0.79, 219/10.77 amount of heat power applied to sections of a metal object by Int. Cl H05!) 5/00, the heating coil is varied according to a predetermined pat- H05b 9/06 tern Electric power applied to the entire shunt coil and heat- Field of Search 2 l 9/ 10.75, ing coil unit is lowered over a period of time to cool the metal 10.77 object progressively along a geometrical axis.

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POWER OF MOLTEN METAL) TOP OF I 5 A 44'? I I v OBJECT l4 LENGTH OBJECT ELECTRIC POWER I msvmsunou OF POWER WlTH I SHUNT COIL vwm'rafl. TH EO DORE R. KENNEDY INDUCTIVE HEATING-COOLING APPARATUS AND METHOD This invention relates to an inductive heating-cooling apparatus and method. More particularly, this invention relates to a method of applying heat to a metal object in such a manner as to cause it to progressively cool along a predetermined geometrical axis.

There are many applications where it is desirable to progressively cool a metal object along a predetermined geometrical axis. For example, progressive cooling is desirable for certain types of ingots and castings to control such unwanted metallurgical phenomena as piping or segregation. Some methods of progressively cooling metal objects have involved the use of induction coils and complex switching mechanisms for incrementally varying the amount of heat applied to particular sections of the metal. Such known techniques suffer from the disadvantage that they cool the ingot or other metal object section by section. Such incremental cooling is effective for eliminating piping and segregation only if carried out over periods of time extending into weeks.

In accordance with the present invention, the disadvantages of known methods and apparatus for progressively cooling metal objects are overcome by providing apparatus for progressively cooling a metal object in a substantially continuous manner and reducing the amount of time required to cool the metal object.

In accordance with the present invention, an inductive hea'ting coil is shunted in such a manner that the heat power applied by difierent sections of the coil varies along the length of the coil. Stated otherwise, the distribution of power applied to the metal objects varies along the length of the coil according to a predetermined pattern. Thereafter, the amount of total electrical power applied to the heating coil is reduced, thereby progressively cooling the coil in a continuous manner.

It is also within the scope of this invention to invert the process described above so that a metal object may be progressively heated in a continuous manner.

The present invention has particular advantage in the cooling of metal ingots withdrawn from induction furnaces. In the past, it has been the practiceto continuously withdraw such metal ingots under vacuum. This creates the need for expensive machinery and awkward handling techniques. The current invention eliminates the need for the use of such vacuum techniques.

It therefore is an object of the present invention to provide a method for continuous and progressive application of heat power to a metal object using an induction coil in a continuous manner.

It is another object of the present invention to provide ap- 'paratus for progressive application of heat power to a metal object in a continuous manner.

Other objects will appear hereinafter.

FIG. 1 is a schematic of an apparatus constructed in accordance with the present invention.

FIG. 2 is a graphical illustration of the concept of the present invention.

For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

Referring now to the drawing in detail, wherein like numerals indicate like elements, there is shown schematically in FIG. 1 an apparatus for progressively heating or cooling a metal object, designated generally as 10.

The apparatus includes an inductive heating coil 12. The heating coil 12 may be conventionally constructed in accordance with well-known principles. It may be any size or shape, but it basically consists of a winding of electrically conductive wire capable of producing a magnetic field whose purpose is to induce electric currents within the metal object 14 for the purpose of heating the same. For purposes of illustrating the present invention, the heating coil 12 is shown in the form of a helix surrounding metal object 14.

The metal object 14 is shown in the form of a solid cyIindri-- cal rod. However, those skilled in the art should recognize that this is merely representative of any electrically conductive metal object. Indeed, the metal object may often be at least partly, and perhaps entirely, molten. Accordingly, an appropriate refractory container for the metal object 14 may also have to be provided. In order to simplify the description of the present invention such a container is not shown.

The heating coil 12 is connected to a power supply 16 by appropriate conductive busses l3 and 15. The power supply 16 includes control means for varying the amount of power applied to the heating coil 12. Since such control means are conventional in the art, they have not been shown in detail.

Appropriate power factor correcting capacitors 18 are connected in parallel with the heating coil 12. Such power factor correcting capacitors are connected in parallel with the heating coil 12 in order to bring its power factor as close to percent as is economically and physically possible.

In the embodiment shown in FIG. 1, the heating coil 12 is provided with taps 20, 22, 24 and 26 at spaced points along its length. The taps 20-26 are shown at equally spaced positions along the length of the heating coil 12 to best illustrate the concept of the present invention. However, those skilled in the art should recognize that the taps 20-26 need not be equally spaced from each other and from the busses l3 and 15.

Each tap 20-26 is connected to one contact of a multiple gang switch 28. Switch 28 serves to connect sections of a shunt coil 30 in parallel with the heating coil 12. As shown, the shunt coil 30 is provided with a plurality of taps 32. Selected taps 32, namely 32A, 32B, 32C and 32D are connected to the multiple gang switch 28. Thus, when switch 28 is closed, sections of the shunt coil 30 are connected in parallel with sections of the heating coil 12.

As shown in FIG. 1, the shunt coil 30 is a uniformly wound inductive coil, preferably having a much larger number of turns per unit length than the heating coil 12. The purpose of the shunt coil 30 is to add inductance in parallel with sections of the heating coil 12. Accordingly, the physical dimensions of the coil are of no importance. Rather, shunt coil 30 should be designed so that a known amount of inductance exists between each of the taps 32. In the embodiment shown the tap to tap inductance is equal. The total inductance of shunt coil 30 is preferably four to five times that of heating coil 12.

In the embodiment illustrated in FIG. 1, no inductance is connected across the heating coil between tap 20 and bus 13. Four units of inductance derived from shunt coil 30 are connected across heating coil 12 between taps 20 and 22; three units of induction are connected across heating coil 12 between taps 22 and 24; two units of inductance are connected across heating coil 12 between taps 24 and 26; and one unit of inductance is connected across heating coil 12 between tap 26 and bus 15. Thus, there is a changing pattern of inductance connected across different sections of the heating coil 12. If the combination of heating coil 12 and shunt coil 30 be considered as a unit when the switch 28 is closed, clearly the circuit impedance varies from parallel connected section to parallel connected section. Thus, the impedance varies in accordance with a predetennined pattern.

The manner in which the impedance is distributed through the circuit, also determines the manner in which power derived from power supply 16 is distributed along the heating coil 12. In the illustrated embodiment, the amount of impedance, hence power, varies in a uniform manner from section to section. Of course, other impedance patterns could be established as desired. It is simply a matter of choosing a particular set of taps 32 on shunt coil 30. Still further, the taps 20-26 on heating coil 12 need not be evenly distributed. It should also be recognized that the division of the heating coil 12 into five sections by the four gang switch 28 is for purposes of illustration. Any number of taps could be used as desired.

When power is applied from power supply 16 with the switch 28 open, as shown, heating coil 12 uniformly applies power to the metal object 14. When the switch 28 is closed,

the distribution of power is varied according to a pattern determined by the selection of tapping points on heating coil 12 and shunt coil 30. This is graphically illustrated in FIG. 2. Thus, the ordinate of the graph represents the length of the metal object 14, and the abscissa of the graph represents the electric power. A family of curves 40, which in the illustrated embodiment are straight lines, each represent the distribution of electrical power along the length of the heating coil 12. Clearly, more electrical power, and hence heating power, is applied near the top of the heating coil 12 than near its bottom. Accordingly, heat is being applied to the metal object 14 at a much higher rate near its top than near its bottom. Of course, the distribution of temperature along the metal object 14 is proportional to the distribution of power.

From the foregoing, it should be recognized that the connection of the shunt coil 30 to the heating coil 12 establishes the slope of the curve 40. Curve 40 is made to approximate a straight line by appropriately choosing the number and spacing of tapping points on shunt coil 30 and heating coil 12.

Once the switch 28 has been closed, distribution of power is established. Thereafter, the metal object can be continuously cooled in a progressive manner. This is best understood by way of example.

Let it be assumed that it is desired to cool a metal ingot which has just been removed in a molten condition from a furnace. The furnace itself may be an induction or consumable electrode furnace. The ingot may have been poured or it may have been removed from the furnace in the manner of a continuous casting. Regardless, it is desirable that the ingot be cooled in a continuous manner. By observing the right-handmost one of the family of curves 40, it will be observed that with the switch 28 closed, the distribution of power applied along the length of metal object 14 is such that its topmost portion has heat applied at such a rate that its temperature is maintained above the melting point. The amount of power sufficient to maintain the temperature above the melting point is represented by the dash line 42. All other portions of the metal object 14 have power applied at progressively smaller rates.

Prior to closing the switch 22, the power applied to the heating coil 12 is sufficient to maintain the temperature of the metal object at or above its melting point. The dash line 42 represents this amount of power. After the switch 28 is closed, the distribution of power along the length of the heating coil 12, and hence along the length of the metal object 14, assumes the condition represented by the right-handmost curve 40. All portions of the metal object 14 immediately begin to cool until the temperature along the metal object is distributed in a straight line condition proportional to the power distribution.

Thereafter, the controls in power supply 16 are operated and the electric power is progressively reduced. This progressive reduction of power is represented by the successive curves 40. At some point in time the power will be reduced sufficiently so that one of the curves 40, namely curve 40A will cross into the region in which the metal object 14 becomes fully solidified. This is indicated by the line 44, marked solidification power. Thus, power levels below the solidification power do not apply enough heat to the coil to prevent it from solidifying. As shown in FIG. 2, only the bottommost portion of the curve 40A has crossed the line 44. Ac cordingly, only the bottom-most part of the metal object 14 has become solidified. With each successive reduction in power, a larger portion of the metal object has less than solidification power applied to it. Thus, curve 408 indicates that a substantial bottom portion of the metal object is below the solidification power level. Curve 40C shows that almost two-thirds of the metal object is below the solidification power level.

By controlling the reduction of power, and spacing each successive reduction in power as close together as desired, the metal object 14 is caused to solidify in a continuous and progressive manner. The slope of curves 40 determines the change in power per unit length for each successive reduction.

Of course, the tapping points chosen on the shunt coil 30 and heating coil 12 sets in the slope. The slope itself may be varied as required by metallurgical considerations. Still further, the curves 40 can be changed from straight line to other configurations if desired.

From the foregoing, itshould be apparent that an apparatus and method for providing continuous and progressive cooling of the metal object has been provided. It should also be obvious that the process can be reversed for the purpose of heating the object in a continuous and progressive manner. Still further, those skilled in the art should recognize the other variations in the control of the electrical power and the power distribution will permit varying forms of progressive heating and/or cooling of metal objects.

The function of the shunt coil 30 is to modify the equivalent inductance from section to section within the heating coil 12. The shunt coil 30 preferably has an inductance which is several times the inductance of heating coil 12. Those skilled in the art will recognize that other devices for modifying the equivalent inductance from section to section in heating coil 12 can be provided. For example, a group of saturable reactors could be substituted for the shunt coil 30. Such saturable reactors have the advantage of being much more flexible in providing the power distribution. However, they are also substantially more expensive, and hence may not in some circumstances be economically justifiable.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

1 claim:

1. Apparatus for controlling a time dependent change of state at each point along the length of an electrical conductive object by progressively changing its temperature, comprising:

a. an induction heating coil of uniform inductance per unit length operatively associated with said object, and having spaced taps along the length thereof;

a plurality of compensation impedances having different values of reactance;

c. switch means for selectively connecting individual induc tors across said taps so that, starting at one end of the coil, there is an increase in the effective inductance between successive taps on said coil due to the reactance of the impedance in parallel with the inductance of the portion of said heating coil between the taps;

d. means to connect an alternating source of electrical power across said heating coil for causing the latter to establish a predetermined temperature gradient along the length of said object; and

e. control means operable to selectively change the level of power applied across said heating coils for progressively changing the temperature of the object at each point along its length at a rate dependent on the speed with which the desired change of state takes place at each such point.

2. Apparatus according to claim 1 wherein said compensation impedances are inductors that are a part of a shunt coil, one end of which is connected to said one end of the coil, said shunt coil being tapped at locations which establish different values of inductance between taps, and said switch means selectively connects the taps of said shunt coil to the taps of said heating coil.

3. A method for causing a time dependent change of state at each point along the length of an electrical conducting object by progressively changing its temperature along its geometric axis comprising the steps of:

a. placing said object in an induction heating coil whose axis is coincident with said geometric axis;

b. shunting said induction heating coil along the length thereof with compensation impedances so that the effective inductance of the shunted heating coil monotonically increases from one end to the other whereby the effective induction gradient of said coil establishes a corresponding applied to the shunted coil for progressively changing the temperature gradient in the object along its geometric temperature of the object at each point along its length at axis when electrical power is applied to said shunted coil; 3 dependent P the speed Wlth whfch the desired and change of state takes place at each such point.

c. selectively changing the rate at which electrical power is 

1. Apparatus for controlling a time dependent change of state at each point along the length of an electrical conductive object by progressively changing its temperature, comprising: a. an induction heating coil of uniform inductance per unit length operatively associated with said object, and having spaced taps along the length thereof; b. a plurality of compensation impedances having different values of reactance; c. switch means for selectively connecting individual inductors across said taps so that, starting at one end Of the coil, there is an increase in the effective inductance between successive taps on said coil due to the reactance of the impedance in parallel with the inductance of the portion of said heating coil between the taps; d. means to connect an alternating source of electrical power across said heating coil for causing the latter to establish a predetermined temperature gradient along the length of said object; and e. control means operable to selectively change the level of power applied across said heating coils for progressively changing the temperature of the object at each point along its length at a rate dependent on the speed with which the desired change of state takes place at each such point.
 2. Apparatus according to claim 1 wherein said compensation impedances are inductors that are a part of a shunt coil, one end of which is connected to said one end of the coil, said shunt coil being tapped at locations which establish different values of inductance between taps, and said switch means selectively connects the taps of said shunt coil to the taps of said heating coil.
 3. A method for causing a time dependent change of state at each point along the length of an electrical conducting object by progressively changing its temperature along its geometric axis comprising the steps of: a. placing said object in an induction heating coil whose axis is coincident with said geometric axis; b. shunting said induction heating coil along the length thereof with compensation impedances so that the effective inductance of the shunted heating coil monotonically increases from one end to the other whereby the effective induction gradient of said coil establishes a corresponding temperature gradient in the object along its geometric axis when electrical power is applied to said shunted coil; and c. selectively changing the rate at which electrical power is applied to the shunted coil for progressively changing the temperature of the object at each point along its length at a rate dependent upon the speed with which the desired change of state takes place at each such point. 